Optical measurement refers to noncontact measurement utilizing numerous light sources. It often requires at least one lens, a light supply and a detector. It differs from other forms of inspection in that instead of utilizing a tactile measurement technique like a contact probe, it uses either a point of reference (e.g. a crosshair) or a pc to calculate edge detection. Two of its greatest benefits are its capability to measure options too small or fragile to measure by contact, and the fact that it is faster compared to other forms of measurement.
The medical, plastics, aerospace and automotive industries are where optical measurement has, and will continue to have, significant impact. But, in reality, this form of noncontact detection applies to applications across most verticals and sectors. Adopters of contemporary optical measurement units are looking for straightforward-to-use technology that helps the acquisition of more accurate data in less time. As a result, there’s a rising demand for in-line measurement and faster processing of acquired images as well as image stitching capability and bigger fields of view. There’s also a growing demand for modern elements like liquid lenses. But when deciding which—if any—optical measurement devices are best for you, all factors have to be considered.
Profile Projectors/Optical Comparators
You may think of this optical measuring system as a high-accuracy overhead projector much like what schools used within the 1970s, ‘80s and ‘90s. It may well accommodate goal lenses up to 100x magnification, use either contour or surface illumination, and has either a microscope-style stage or metal stage with T-slots that can hold as much as 100 lbs. The stage is married to high-accuracy linear scales, which provide positional feedback, and a crosshair is typically etched onscreen as a measurement reference point. Measurement throughput might be elevated by adding edge detection, usually within the form of an onscreen fiber optic detector.
Operation is fairly straightforward, with a person inserting a workpiece on the stage with the necessary fixturing, then bringing the workpiece into focus by adjusting the Z-axis position. Once there’s a centered image on screen, the person moves the stage so the onscreen reference reticle is aligned with the function of interest. The user then can zero the scales on either the X- or Y-axis and move the stage to the following position on the feature. The size readout will determine the space traveled with increased measurement repeatability made potential with the usage of edge detection software. Final data is stored and analyzed by an optional 2D processor.
Advantages: The design of the target lens, coupled with a screen measurement that may measure 14 inches or larger, means profile projectors typically have a larger discipline of view. Having been a well-known staple for decades, they’re one of the best measurement devices to use. Unlike a measuring microscope, profile projectors are likely to inflict a low level of eye strain. And, overall, they are typically the least expensive option while remaining one of many fastest.
Disadvantages: Profile projectors/optical comparators have a lower optical decision in comparison to measuring microscopes as well as a lack of digital processing capability and low throughput. Lighting options are additionally limited, sometimes only including contour illumination.
Measuring Microscopes
It’s important to point out that measuring microscopes are totally different from traditional microscopes. Unlike a traditional microscope, in a measuring microscope the stage is linked to linear scales that provide positional feedback, and a reticle is either built into the eyepiece itself or located in the light path as a reference point for measurement. In addition, a measuring microscope comprises each in-line illumination for applications that require reflected light and transmitted illumination that permits for contour or profile measurements.
When it comes to operation, measuring microscopes perform in an identical manner to profile projectors. A workpiece is positioned on the stage, and an image of the function of curiosity is then brought into focus by adjusting the coarse and fine focus knob. As soon as a transparent image is viewable, the user aligns the built-in reticle and then moves the stage to the following edge of the feature. The ensuing scale readout shows the space traveled. As with profile projectors, edge detection software can be added to achieve higher accuracy and repeatability towards determining the exact edge of a part.
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